1. Field of the Invention
The invention relates to an apparatus and method for controlling communications between electrical appliances through household power lines.
2. Description of the Related Art
A control system is currently available that controls the operation of household electrical appliances by communicating with those appliances through the electric wires that supply electrical power to the lights and appliances in the home. This control system is called a household power line communication system. That is a control system in which the wires supplying power to the lights and electrical appliances in the home are also used as a communications medium. In this system, each electrical appliance in the home is equipped with a power line communications modem. A centralized control unit is also provided to control communications with and between electrical appliances. For example, the control unit may be able to monitor a condition in which a refrigerator door has been open longer than a specified time duration, and direct a television receiver to display an on-screen warning. Furthermore, Japanese Patent Publication No.2002-84658 shows the system that may be able to control the consumption of electricity by the household electrical appliances in order to keep consumption below an amount contracted with the electric power utility.
However, the household power line communication system has the following problems.
There are no international standards in regard to the use of household power lines for communication purposes. Different countries and even different regions within a country may often use different standards. The reasons for that are because they have their own the frequency bandwidth that can be allocated for power line communications, their own voltage used by electrical appliances, and their own frequency bandwidths already being used for other purposes, such as radio broadcasts. Therefore, establishing an international standard has proven difficult.
In Japan, a domestic operating standard for power line communications has been established through the work of the Echo-net Consortium. However in Europe, while a frequency bandwidth has been established for household power line communications (European Norm 50065-1), a modem modulation method has not been decided for such communication. Moreover, an access protocol (the Carrier Sense Multiple-Access (CSMA)) that is established for avoiding the cross interference of various methods of modulation, such as the cross interference with radio broadcasts, specifies that the frequency bandwidth called the “C” band of 125 to 140 kHz in European Norm 50065-1 should be utilized for power line communications. If one adheres to CSMA, it becomes possible to build a system compatible with various methods of modulation.
Examples of these modulation methods are Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), and Phase Shift Keying (PSK), each having its own advantages and disadvantages.
These modulation methods generally exhibit the following characteristics. The ASK method, while offering the advantage of simple circuit structure, is susceptible to noise interference. The PSK method offers desirable noise resistance characteristics, but requires a complex circuit structure. The FSK method offers characteristics lying between those of the ASK and PSK methods.
As a result of these factors, no standardized method of modulation has been established for power line communications in Europe. Even if one purchases a European electrical appliance with power line communications capability, there is still the problem of a lack of compatibility between electrical appliances because of their use of different modulation methods.
This present invention is provided to solve above problem. The purpose of the invention is to provide a control apparatus and method that can manage all electric appliances in the home through household power line communications, that can be used in Europe where there is no modulation method standard for power line communications systems, and that can manage multiple electrical appliances equipped with modems that may not operate with a common modulation method.